It is known for protective head gear to be worn by people undertaking sports where there is a risk of impact to the head. A range of helmets are produced, usually with a specific sport in mind. For snow sports such as skiing and snow boarding there are two main types of protective helmet. The first of these uses an injection moulded acryonitrile butadiene styrene (ABS) shell having a glued-in liner of expanded polystyrene (EPS). Using ABS provides a strong shell, and this kind of helmet is relatively inexpensive. However, ABS is heavy as well as durable. It is known that heavier helmets can increase the risk of injury to the wearer's head and neck, particularly when it comes to rotational injuries.
A lighter form of helmet can be made by using a vacuum formed polycarbonate (PC) shell. It is also known to line a PC shell with injected EPS, forming a bonded lining. Bonding a liner to a helmet shell in this way improves the structure of the helmet and increases strength. However, while PC can be used to form a lighter shell than ABS, it is not as durable and can be more easily damaged on impact.
What is required is a helmet with an improved strength to weight ratio; that is one having optimum structural strength and impact resistance while being as light as possible. Such a helmet should also meet appropriate safety standards and be inexpensive to produce.